FR2477009A1 - Ligament or tendon prosthesis - is polyethylene terephthalate strip held lengthwise while treated with shrinking agent to reduce lengthwise extensibility - Google Patents

Abstract

Prosthesis for repairing or replacing a ligament or tendon is prepared by treating a strip of polyethylene terephthalate with shrinking agent while preventing longitudinal shrinkage for a time such that lengthwise extensibility is reduced. The strip may be woven or may be a circularly- or warp-knit flattened tube with one or both surfaces velour and at least one lengthwise ridge extending from a surface. The shrinking agent is pref. CH2Cl2, alone or combined with NO2, and treatment reduces extensibility by >=50%.

Description

 The need for artificial splints or ligaments to replace or supplement natural ligaments and tendons when these ligaments and tendons are damaged, usually accidentally, is widespread enough that conferences have been held on the subject and that the problem has been discussed in reports from orthopedic surgeons. We can cite, as an example of a frequent injury requiring a device of this kind for a satisfactory surgical repair, an acromioclavicular displacement, where the injury is produced by falling on the point of the shoulder with the arm in position. adduction. By this action, one or more of the ligaments confining the acromioclavicular joint may rupture, and repair or surgical repair using an appropriate splinting device, to give damaged ligaments internal support, is frequently indicated .

Other ligaments such as the medial cruciform and anterior cruciate ligaments can similarly be repaired or rehabilitated.

 These constructions can also be useful in a surgical reconstruction of damaged tendons like the Achilles tendon and the tendon or patellar ligament, and possibly the digital flexor tendons.

Tendons have a very low capacity for self-regeneration, and thus they require very long periods to perform their own repair without the aid of a prosthetic implant.

Surgeons experienced in the repair of ligaments and tendons have recommended several desirable characteristics for the materials (or constructions) to be applied as internal splints.
1. The material must be able to exert a mechanical resistance equal to that of the damaged ligament, at least under an activity under moderate stress.

 2. It must have sufficient strength & elongation under stress, to maintain its mechanical efficiency.

 3. The material must be acceptable for permanent implantation in the human body, preferably without the need for removal by a second operation.

An important condition for good acceptability is that the material is sufficiently porous to allow invasion by the host tissues.

 4. The fishplate must allow early activity.

Mainly for the desirable characteristics of resistance, porosity and flexibility, the attention of the surgeons was directed to tubular constructions in Dacron (polyethylene terephthalate, Du
Bridge) knitted and woven, used in vascular surgery as a possible building material for ligament splints. However, it has been found that Dacron prostheses in the constructions usually used have an inappropriate resistance to elongation under stress, the elongation reaching values of up to 150%. Furthermore, it is very desirable that the cross section of the prostheses is such that they are invaded by the host tissue and that there is a housing for the formation of a living structure which can complete the prosthesis.

 As is evident, a structure offering a higher resistance to elongation and which is rigid enough for a tubular structure with an open orifice to be produced is quite desirable.

 To prepare a prosthesis according to the invention, a strip of fabric is prevented from shrinking in the longitudinal direction and then it is treated with a shrinking agent under conditions such that the extensibility of the strip of fabric is reduced by at least approximately 50%.

The strip can be flat or tubular, generally in flattened tubular form. To give it its rigidity, the strip can be formed into a tube, slid on a mandrel and then hardened or taken hot, for example by treatment at around 1210C for about 3 minutes. In addition to giving it its rigidity, the heat setting operation forms an open orifice for invasion by the host tissue.

 In a preferred form, at least one surface of the strip is in velvet construction, the velvet surface facilitating the adhesion of the host tissue. Likewise, the fabric may be of a woven construction, knitted in the round or in warp knitting.

 Consequently, the present invention relates to a method for preparing a Dacron prosthesis having reduced extensibility, suitable for implantation in a patient to replace or supplement or repair a damaged ligament or tendon.

 Another subject of the present invention is a process for preparing a prosthesis of increased rigidity, having an open orifice, for repairing, completing or replacing a damaged ligament or tendon in a patient.

 Another subject of the present invention is a method of treating a patient suffering from a damaged ligament or tendon, this treatment consisting in using a Dacron prosthesis having improved properties, more particularly with regard to extensibility, and facilitating the growth of host tissue.

 Another subject of the present invention is a prosthesis capable of repairing, completing or replacing a damaged ligament or tendon.

 An important object of the present invention is a prosthesis capable of repairing, supplementing or replacing a damaged ligament or tendon in a patient, this prosthesis having reduced extensibility and better properties compared to the growth of the host tissue.

The invention will be better understood, and other objects, characteristics, details and advantages thereof will appear more clearly during the explanatory description which will follow, made with reference to the appended schematic drawings given solely by way of example illustrating several embodiments of the invention and in which
- Figure i shows a dacron strip under restraint, in preparation for treatment with a shrinking agent;
- Figure 2 is a section of a Dacron strip formed into a tube;
- Figure 3 is a section of an initially flattened tubular strip formed into a tube & two walls;
- Figure 4 is a section of a Dacron tube according to the present invention, this tube having longitudinal ridges on its surface; and
- Figure 5 is a graph showing the elongation under stress, of an artificial ligament prepared according to the invention (A) and of a vascular graft prepared by traditional methods (B), the stress being indicated on the ordinate axis and elongation on the abscissa axis.

 The Dacron fabric to be used in the process according to the invention may initially have the shape of a flat strip or may be a flattened tube prepared by weaving, knitting in the round or chaste knitting. If the material is a flat band, it can be woven or warp knitted. If the material is clean, as received, it may be subjected to shrinkage or compaction treatment as received. Otherwise, it is cleaned by washing or traditional cleaning to remove the primer, oils or other foreign matter.

 It is usual to pack knitted Dacron products by a commonly used process, the preferred shrinking agents being CH2Cl2 and CH2Cl2 in combination with NO2. Usually, the material is simply exposed to the shrinkage agent to effect the desired degree of compaction, the main objective being to reduce the size of the openings between the threads making up the fabric. However, these fabrics, following the shrinking operation, have a degree of extensibility indicated by the lower curve of Figure 5, which is so important that a splice made of such a fabric can not provide support It has been found that by subjecting the fabric to packing with the shrinking agent under restraint in the longitudinal direction, this greatly reduces the extensibility of the packed fabric.

In general, the elongation at a given stress should be reduced by at least about 50%. Preferably, the elongation should be reduced by at least about 60%.

Thus, under a constraint which can produce, in a traditionally narrowed fabric, an elongation of 150%, the elongation of the fabric treated according to the invention will only be of the order of 60% as can be seen by the upper curve of Figure 5.

 Figure 1 schematically shows a strip of fabric 11 held in a rigid frame 12 between clamps 13. The entire frame with the strip 11 kept under restraint can be placed in a container, not shown, for treatment by the shrinking agent in the desired temperature and humidity conditions.

 The fabric strip can be either flat or tubular in construction, during the compaction process.

However, it has been found that it is desirable for the prosthesis to be implanted in a patient to be tubular, that is, to have an open port. The fabric strip, assuming that the keel is initially of tubular construction, for example when it is knitted in the round, woven or warp knitted in tubular form, and whether or not it is kept in open tubular form during the packing process, will collapse when it is removed from the hold. Consequently, the strip is placed on a mandrel and is taken hot to give it a certain rigidity, the amount of rigidity produced being sufficient for an open orifice to be maintained. Figure 2 shows how a flat strip can be formed into a cylinder 16 by sewing its two selvedges 17 and 18 with Dacron 19 wire. This tubular section can then be placed on a mandrel and taken with the heat of one way # usual, for example by heating for 3 minutes & 1210C.

 Figure 3 shows another suitable construction, the strip in this case being a flattened woven or knitted tube, which is then formed into a double-walled cylinder 21 by sewing the edges 22 and 23 by means of a wire 24 Dacron. In this case, the edges 22 and 23 are actually folds rather than actual edges.

 The size of the tendons to be completed or repaired or replaced is between approximately 2 mm in diameter and approximately 10 mm in diameter. For the smallest tendons, the construction of Figure 2 is generally suitable with regard to stiffness. For somewhat larger tendons, say on the order of 3 mm to about 6 mm, the two-wall construction of Figure 3 can provide stiffness - appropriate. For larger tendons, we prefer the construction shown on the prosthesis of Figure 4. This construction begins with a flattened tube having a circumference or, rather, a periphery, in cross section, between about 30 and about 70 mm. starting from the flattened tube, the material being indicated by the mark 26, the two layers forming the flattened tube are sewn together longitudinally along lines located at approximately 2 mm from each edge, using a Dacron 27 thread. The tube is then folded so that each original crest 28 is between new folds 29. The new folds are likewise sewn together longitudinally using Dacron threads 30. The tube, now having four crests, is compacted by chemical treatment then it is taken hot on a mandrel as described above.

Obviously the above process can be modified to produce any number of ridges, from one to the point where the entire circumference of the tube consists of ridges with virtually no tube between them. However, generally three to about six peaks are preferred, with the largest number of peaks being used with the larger tubes. Likewise, as can be easily seen, it is possible to start with the double-wall construction of FIG. 3 and then to incorporate ridges therein. Furthermore, the height of the ridges is not limited to 2 mm, but this value has proved to be practical for the sewing step, and there is little increase in rigidity obtained by a corresponding increase in height. ridges.

 The open or light orifice of the constructions of Figures 2 to 4, as already noted, is intended to allow the growth of body tissue. Such a fabric must be anchored to the Dacron strip, according to the method of the invention. Anchoring is facilitated If at least one surface has a well-known velvet structure. This structure is indicated in Figure 4 by the outer loop 32 and the inner loop 33. Tests have shown that the velvet construction accelerates the growth of body tissue and provides them with a firm anchorage. Twenty-five patients undergoing type III separation from the acromioclavicular Articulatlon have obtained clinical results. All of these patients were treated with the internal fixation method. The patients were between the ages of seventeen and sixty-seven, with an average of thirty-three years. The patients were followed up for periods of between twelve months and six years, the average period being thirty-five months. The mechanism of injury was similar for all patients in this series, that is, a fall on the tip of the shoulder. Twenty-three of the twenty-five patients were examined and assessed, while two of the patients were assessed by telephone.

 Among the patients evaluated, it was noted that more than half did not suffer from any kind of pain.

The others, with one exception, all had occasional discomfort that did not compromise their activity.

The patient who had slight discomfort worked at weights, and only felt pain when he actually lifted weights, but otherwise had no activity limits. The function of all patients was normal, and no deformity was noted. Three of the patients presented with a reduction in internal rotation, this internal rotation being reduced to 700 compared to the normal internal rotation of 900. As can be seen from the above sample of the results obtained with prostheses according to the invention, the prosthesis lasts for at least six years, causes minimal discomfort, allows the subject a good range of movement, and produces no deformity following surgery.

 Many patients can return to relatively normal activity within two weeks. This return to early activity decreases the morbidity associated with this type of injury.

 Of course, the invention is in no way limited to the embodiments described and shown which have been given only by way of example. In particular, it includes all the means constituting technical equivalents of the means described as well as their combinations if these are executed according to its spirit of implementation in the context of protection as claimed.

Claims (17)

 1.- A method of preparing a prosthesis to repair, complete or replace a damaged ligament or tendon, characterized in that it comprises the step of treating an elongated strip of polyethylene terephthalate, called "Dacron", having two surfaces , by means of a shrinking agent under conditions such that only longitudinal shrinkage is prevented, said treatment being continued for a period long enough to effect a substantial reduction in the longitudinal extensibility of said strip.  2.- Method according to claim 1, characterized in that it further comprises the steps of putting the aforementioned strip in tubular form following its treatment with the aforementioned shrinking agent, of placing said strip in tubular form on a mandrel and hot setting said strip for a period of time long enough at a temperature high enough to harden or heat set said strip in a tubular form.  3.- Method according to claim 2, characterized in that the aforementioned strip is initially a single layer with two long selvedges and in that it is brought in tubular form by joining said long selvedges.  4.- Method according to claim 2, characterized in that the aforementioned strip is initially a flattened tube and knitted in the round.  5.- Method according to claim 2, characterized in that the aforementioned strip is initially a flattened tube and warp knitted.  6.- Method according to claim 2, characterized in that the aforementioned strip in tubular form has at least one longitudinal ridge which extends from one of its surfaces.  7.- Method according to claim 1, characterized in that at least one of the surfaces of the aforementioned strip is a velvet.  8.- Method according to claim 1, characterized in that the two surfaces of the aforementioned strip are velvet.  9.- Method according to claim 1, characterized in that the aforementioned shrinking agent is CH2Cl2.  10.- Method according to claim 1, characterized in that the aforementioned shrinking agent is a combination of CH2Cl2 and NO2.  11.- Method according to claim 1, characterized in that the aforementioned treatment with a shrinking agent is carried out under conditions such that this reduces the extensibility of the aforementioned strip by at least about 50%.  12.- A prosthesis suitable for repairing a damaged ligament or tendon, characterized in that it comprises a strip of polyethylene terephthalate fabric of reduced stretch in the longitudinal direction, the term "fabric" designating woven products, knitted in the round and knit channe.  13. A prosthesis according to claim 12, characterized in that the above-mentioned fabric has at least one velvet surface.  14. A prosthesis according to claim 12, characterized in that the aforementioned strip has an orifice open in the longitudinal direction.  15. A prosthesis according to claim 12, characterized in that the aforementioned strip has a tubular part and comprises at least one crest extending longitudinally on the surface of said tubular part.  16. A prosthesis according to claim 12, characterized in that the extensibility of the aforementioned artificial ligament is characteristic of a strip of polyethylene terephthalate having been treated with a shrinking agent under conditions such that this reduces the extensibility of minus about 50%.  17. A prosthesis according to claim 12, characterized in that the aforementioned strip is in tubular form with an open orifice and has a characteristic  stiffness of a strip which has been treated with a shrinking agent under conditions such as to reduce its shrinkage by at least about 50%, and heat cured on a mandrel.